NEW YORK — Alex Rodriguez is going on the 15-day disabled list with a strained right quadriceps, leaving the New York Yankees without two of their most important players.

Rodriguez joins injured catcher Jorge Posada on the DL. The Yankees are waiting for additional opinions on Posada's ailing throwing shoulder before determining whether he needs surgery.

A three-time AL MVP, Rodriguez was sent for an MRI exam today that revealed a Grade 2 strain. He was put on the DL for the first time since July 2000 with Seattle, when he had a strained right knee.

This is Rodriguez's fifth career trip to the disabled list.

"If it's a Grade 2, it's going to be at least the two weeks. That's why we're doing it," general manager Brian Cashman said.

The Yankees said it hadn't yet been determined whether Rodriguez would officially be placed on the disabled list Tuesday or Wednesday. Regardless, his stint on the DL can begin Tuesday because the team played without him — and Posada — in a 6-4 loss to the Detroit Tigers.

Rodriguez has been bothered by the injury since getting hurt April 20 in Baltimore. The third baseman missed three games last week, then returned for a four-game series at Cleveland. But he was removed for a pinch hitter in the eighth inning of Monday night's 5-2 win over the Indians and said he felt a "pull" while running the bases.

Yankees manager Joe Girardi said the team was surprised to learn the strain was so severe. Rodriguez was not available to reporters after Tuesday night's loss.

"He's a hard guy to replace," Girardi said. "We have to find a way to get it done."

Morgan Ensberg started in Rodriguez's place at third base Tuesday night.

"Hopefully, it'll be no more than the 15 days," Cashman said. "But we've got to get it right."

Posada, placed on the disabled list Monday for the first time in his career, was examined by orthopedist Dr. James Andrews in Alabama. Girardi said the scans from those tests were being sent to Cincinnati Reds team physician Dr. Timothy Kremchek, a shoulder specialist.

Posada also was scheduled to be examined Tuesday night by Yankees physician Dr. Stuart Hershon, and on Thursday by New York Mets medical director Dr. David Altchek.

"Till all the doctors weigh in, I'm not going to guess and speculate. When they give me concrete information I'll be sure to share it," Posada said through club spokesman Jason Zillo.

Girardi said he remains optimistic that Posada won't need surgery, which would sideline the durable catcher for an extended period. For now, his injury has been termed a strained right shoulder.

"He had a good meeting with Andrews. The films are being sent to Kremchek and so we'll wait for that and we'll go from there," Girardi said.

The Yankees hope to get Kremchek's opinion in the next few days.

Chris Stewart made his first start behind the plate for New York against the Tigers, one day after being called up from the minors.

Still hoping to avoid season-ending surgery, reliever Brian Bruney went for a third opinion on his injured right foot and was waiting for the results. Bruney is on the 15-day DL.